This invention relates to a plate-type heat exchanger comprising a required number of plates laminated through gaskets and is used in the fields of food and medicines where the use of an adhesive agent should be avoided in attaching the gaskets to the plates and in the field of general chemistry where improvements in gasket replacement maintenance is desired.
Generally, a plate-type heat exchanger comprises a required number of plates each having a heat transfer surface formed with a suitable unevenness pattern, said plates being laminated through gaskets to define a plurality of channels between adjacent plates, with two types of mediums flowing through alternate channels.
FIG. 9 is a partial perspective view showing a concrete example of a typical plate-type heat exchanger, wherein the numeral 1 denotes plates each having a heat transfer surface 2 with a suitable unevenness pattern (not shown) and having holes 3, 4, 5, 6 at four corners, and gaskets 7 of synthetic rubber or other elastic material having heat resistance are mounted, each gasket surrounding the associated heat transfer surface 2 in such a manner as to establish communication between the holes 3 and 4 and close the other holes 5 and 6. A required number of such plates 1 are alternately turned upside down and laminated to define a channel 8 for a medium a and a channel 9 for a medium b.
In such plate-type heat exchanger, as shown in FIG. 10, the gasket 7 is fitted in a gasket groove 10 formed in the peripheral edge of the plate 1. The plates 1 are laminated, whereby the gaskets 7 are pressed against the rear surfaces of the gasket grooves 10 of adjacent plates 1 to define sealed channels 8 and 9 between the plates 1, thus forming a sealing construction which prevents the mediums from leaking outside.
Heretofore, it has been common practice to fix said gaskets in the gasket grooves 10 by an adhesive agent. That is, since such adhesive agent suitably fixes the gaskets 7 in the gasket grooves 10 but allows the relatively easy removal of the gaskets when it is necessary to replace them, it has been generally used for fixing the gaskets in the gasket groove 10. When it is desired to adhesively fix the gaskets 7 in the gasket grooves 10 of the plates 1, however, it is necessary to wash the oil and grease and other extraneous substances, which hinder adhesion, off the surfaces of the plates 1 in advance of application of an adhesive agent. Further, application, drying and aging of an adhesive agent take time and there has been a need for maintenance operation including careful cleaning of the old adhesive agent off the gasket grooves 10 in advance of adhesion of fresh gaskets 7 to replace the old gaskets 7. Besides this, in the case where heat exchange is effected for fluids for food and medicines, migration of an adhesive agent sometimes becomes a problem. Therefore, it has been desired to fix the gaskets 7 in the gasket grooves 10 of the plates 1 without using any adhesive agent.
According to a known arrangement for attaching the gaskets 7 to the gasket grooves 10 without using any adhesive agent, as shown in FIGS. 11 through 13, fixing tabs 7b are integrally fixed at suitable intervals to the liquid-noncontacted peripheral side surface of the gasket body of a gasket 7 and a fixing projection 7c is integrally fixed to each fixing tab 7b, while the liquid-noncontacted peripheral side surface of each gasket groove 10 of the plate 1 is recessed to form a gasket fixing insertion portion 10a corresponding to said fixing tab 7b and the bottom of said gasket fixing insertion portion 10a is formed with a fitting hole 10b associated with said fixing projection 7c to receive the latter, said fixing projection 7c of said tab 7b being force-fitted in said fitting hole 10b of the fixing insertion portion 10a, thereby fixing the gasket 7 to the gasket groove 10 of the plate 1.
According to the means described above, the fixing of the gasket 7 to the gasket groove 10 of the plate 1 without using any adhesive agent becomes possible, but there has been the following problem.
The material for gaskets to be used in plate-type heat exchangers is suitably selected according to the temperature, pressure and liquids to be used. Thus, many gasket materials have been required and used.
First, in the case of a gasket 7 which is made of an elastic material having heat resistance, such as synthetic rubber, since the amount of shrinkage taking place during manufacture due to difference in material, if the same metal mold is used to produce gaskets of synthetic rubber, the length always differs. Even if the same material is used, when the production lot differs, a scatter occurs in the length of the gasket body 7a; furthermore, such dimensional scatter is not constant on the entire periphery of the gasket body 7a but takes place locally. Therefore, in the case of the conventional gasket 7 in which the fixing point of the fixing tab 7b is set at a single point, the scatter in the length of the gasket body 7a cannot be accommodated in the fixing operation. Therefore, in the case where the gasket body 7a of the gasket 7 is long, when the gasket 7 is fixed in the gasket groove 10 of the plate 1, the gasket body 7a is locally bent, as shown in FIG. 14 at a, and is raised from the gasket groove 10 of the plate 1, so that when the plates 1 are clamped for lamination, the gasket 7 is not received in the predetermined position in the gasket groove 10 of the plate 1; thus, the sealing property becomes a problem. Further, in the case where the gasket body 7a is short, as shown in FIG. 14 at b, the fixing of the gasket 7 in the gasket groove 10 is effected with the fixing tab 7b positioned in the bent state in the gasket fixing insertion portion 10a of the gasket groove 10. Thus, the operability for fixing the gasket 7 in the gasket groove 10 is degraded, and the gasket body 7a is raised from the gasket groove 10 by the bent fixing tab 7b, so that when the plates 1 are laminated, the gasket 7 is not received in the gasket groove 10 of the plate 1, offering a problem of sealing quality. Further, since the gasket 7 is merely integrally formed with the fixing tab 7b projecting from the gasket body 7a with only a limited area of junction, the fixing tab 7b has a limited strength, tending to bend with respect to the gasket body 7a. Thus, to achieve firm fixing of the gasket 7 in the gasket groove 10 of the plate 1, many fixing tabs 7b must be formed with a short pitch, and the plate processing equipment and the gasket processing time are increased, leading to a cost increase. Further, the fixing tab 7b of the gasket 7 tends to bend with respect to the gasket body 7a and the fixing projection 7c is integrally formed with the fixing projection 7c on the rear surface of the front end thereof; therefore, when a plurality of gaskets 7 are bundled during manufacture or handling, the fixing tabs 7b and fixing projections 7c interfere with each other, making handling inconvenient or damaging the fixing tabs 7b. Further, since the fixing force created by the force-fit between the fixing projection 7c integrally formed on the rear surface of the front end of the fixing tab 7b of the gasket 7 and the fitting hole 10b formed in the plate 1 is low, the gasket 7 tends to be disengaged from the plate; thus, there has been a problem of sealing quality.
This invention has been accomplished in view of the aforesaid problems to the conventional plate-type heat exchanger and has for its object the provision of a plate-type heat exchanger wherein the operation for fixing gaskets in gaskets grooves in plates is improved and high fixing force is obtained and the gaskets are seldom damaged.